1. Field of the Invention
The present invention relates to an image pickup unit for endoscope including an image pickup device, and an endoscope.
2. Description of the Related Art
In medical fields and industrial fields, for example, endoscopes have been used in order to observe a region which is difficult to observe such as an inside of a living body or an inside of a construction, and such endoscopes include an insertion portion which can be introduced from outside into inside of a living body or a construction, and also includes, at the insertion portion, an image pickup unit for picking up an optical image.
An image pickup unit for endoscope includes: an objective optical system member constituted of a lens which forms an image of an object; and an image pickup device such as a CCD (charge coupled device) or a CMOS (Complementary Metal-Oxide Semiconductor) sensor disposed on an image-forming surface of the objective optical system member.
An image pickup unit for endoscope is generally configured such that the camera control unit is provided outside the insertion portion, since there is a need for reducing the size of the outer diameter of the insertion portion. Such a configuration of an image pickup apparatus provided to an endoscope is generally called as a camera head separation type image pickup apparatus or the like. In an endoscope, signal communication between the image pickup device and the camera control unit is performed through a relatively long transmission cable of ten and several centimeters to several meters, for example.
In such an endoscope, delay of a video signal outputted from the image pickup device to the camera control unit is likely to occur due to a variation in length of a transmission cable and a variation in electrical performances of the incorporated electronic components, for example. In order to address such a problem, it is necessary to synchronize operation of the image pickup device with operation of the camera control unit by performing video phase adjustment such as adjustment of a sampling timing with respect to a phase of a video signal using the camera control unit and other electric circuits, for example. In order to perform video phase adjustment, a method of providing a timing generator on the image pickup device side, or a method of reducing a variation in length of a transmission cable and a variation in electrical performances of incorporated electronic components can be considered, for example. However, if a timing generator is provided on the image pickup device side, the size of the electronic circuit around the image pickup device increases, which results in an increase in the diameter of the insertion portion of the endoscope. Furthermore, in order to reduce tolerances of the transmission cable and the incorporated electronic components, it is necessary to increase the sizes of the cable and the electronic components, and also in such a case, the size of the insertion portion of the endoscope increases.
Therefore, Japanese Patent Application Laid-Open Publication No. 5-308579, for example, discloses a camera head separation type image pickup apparatus in which a technology of allowing a signal as an indicator to be outputted from a predetermined pixel in an optical black region of an image pickup device and adjusting sampling timings of the camera control unit and other circuits by using the signal as the indicator, to synchronize the image pickup device and the camera control unit is disclosed.